Tailoring Interfacial Performance of UHMW PE Fiber Composites Via Covalent Bonding Assisted by Plasma Surface Treatments

Fiber-reinforced polymer composites are lightweight materials that can possess excellent mechanical properties. As a result, these materials can be found in many applications where these properties are of importance. Composite mechanical behavior, like strength and fracture toughness, is known to be dependent on the fiber-matrix interface. Composites made with ultra-high molecular weight polyethylene (UHMW PE) fibers and thermosetting matrices like epoxies have shown poor interfacial performance. This is a result of poor adhesion attributed to the chemical inertness, poor wettability and low surface energy of the fiber. Surface treatments employed through the use of non-thermal plasmas have provided the means of overcoming these limitations by increasing chemical and physical interactions of the fiber to the matrix. However, the relative importance that physical and chemical interactions have for improving interfacial performance has to this point not been clear.;The focus of this dissertation is to gain a better understanding of how surface characteristics chemical and physical of the fiber govern the interfacial properties at the fiber-matrix interface. Atmospheric pressure non-thermal plasma surface treatments were implemented to functionalize the surface of UHMW PE. Conventionally, low pressure plasma systems have been utilized for surface treatments; however, atmospheric pressure systems have proven to be a viable alternative. The effectiveness of the plasma treatments were evaluated using various surface analytical techniques such as SEM, ATR-FTIR, XPS, AFM, contact angle, and titrations. Chemical and physical characteristics of the fiber were correlated to interfacial properties measured using the single fiber microdroplet test. Observations strongly substantiate that covalent bonding is the dominant contributing factor for observed improvements of interfacial properties, This was further supported by results of grafting studies designed to control reactivity and reactive site surface concentration. Overall, this work has shown that covalent bonding is the governing factor controlling interfacial behavior in UHMW PE fiber-epoxy composites and that it can be used effectively to tailor performance.